Ok so I purchased a used set of weld pro-star drag wheels 15" x 10", but they don't quite clear the calipers on my 12' GT I was wondering how I figure out what size spacer I need so I can use them at the strip next time I go.

i disagree with LOWFLY. A dude on the mach 1 forum is running spacers at the rear and hes puttin down over 500 rwhp and hasnt had any problems. I would think a small 5mm hubcentric spacer would be perfect for ya. I would assume your clearance issue is minimal and these spacers usually do the trick.

Spacer put added stress on studs due to the length and the hub due to it possibilty of not being hubcentric. Not being hubcentric can also cause wobble or wicked vibration on a wheel because its not balanced true to the wheel, it dont always happen but it has. The solution is longer studs like ARP race studs and a true hubcentric spacer. The best solution is a new wheel with proper offset of backspacing. The wheel is machined to pose as the spacers assisted space but doesnt use anymore stud than a normal wheel.

To help figure the size of spacer, use a hand full of washers as shims to gage what it will take to get the clearance. Then remove the wheel measure the thickness of the washers and you have the thickness. Add that thickness to the stock studs to get the new stud length.

Ok so I purchased a used set of weld pro-star drag wheels 15" x 10", but they don't quite clear the calipers on my 12' GT I was wondering how I figure out what size spacer I need so I can use them at the strip next time I go.

To help figure the size of spacer, use a hand full of washers as shims to gage what it will take to get the clearance. Then remove the wheel measure the thickness of the washers and you have the thickness. Add that thickness to the stock studs to get the new stud length.

I put the small spacers on my 2012 GT rear stock rims and had problems. I ended up with problems with the threads on the wheel studs along w/ some minor balance problems because they are not hubcentric... I'm not suggesting this, but I'll raise an idea and question that might help your situation; Can you slightly modify the back side of the rim to create clearance?

A spacer too thick can cause issues for sure and worse case makn it non hubcentric which IMO should always be avoided. But to say a conservstive 5mm spacer is harmful is taking things a lil to far. Let me ask u this, if someone gets new wheels with smaller offsets tht causes wheels to stick out 5mm more than the stockers is this any worse than using stock wheels w 5mm hubcentric spacers? Just curious

You need to make sure any spacer is hubcentric and make sure you get enough thread engagement on your lug nuts regardless of what spacer you run. Best practice is to press in longer ARP studs and then run the hubcentric spacer you need.